This application claims priority of Korea patent Application No. 2000-68911, filed on Nov. 20, 2000.
(a) Field of the Invention
The present invention relates to a method for controlling fuel supply of a vehicle on acceleration and a system thereof, and more particularly, to a method for controlling fuel supply such that an appropriate fuel supply is achieved quickly on acceleration, and noxious exhaust gasses are reduced and output power of an engine is increased at the same time.
(b) Description of the Related Art
Recent engines of vehicles are provided with an electronic control unit (written as ECU hereinafter), where the ECU, having data of operating conditions such as vehicle speed and engine speed being input, controls fuel supply for the engine by controlling injectors injecting fuel into the engine.
If an engine is accelerated by changing a throttle valve state from throttle valve off-state to throttle valve on-state, the throttle valve off/on-state being a state that the throttle valve is closed/opened, the ECU determines an appropriate amount of fuel to be supplied on acceleration and controls the injectors to inject the determined amount of fuel, the amount of fuel supplied being calculated on the basis of feedback gains.
The feedback gains include a proportional gain (written as P-gain hereinafter) that is proportional to an input signal from an O2 sensor, and an integration gain (written as I-gain hereinafter) that is proportional to an integrated value of the input signal from the O2 sensor. While under acceleration, these feedback gains are still considered to reduce noxious gasses included in exhaust gas.
More specifically, an amount of fuel supplied on acceleration is calculated by adding an acceleration correction value to a base amount of fuel multiplied by a short-term correction value and a long-term correction value, the acceleration correction value being determined through a predetermined process.
The base amount of fuel is an amount of fuel corresponding to a theoretical air/fuel ratio provided that a feedback signal is not considered. The short-term correction value is a correction value calculated on the basis of the real time I-gain and P-gain of the signal from the O2 sensor, and the long-term correction value is a correction value calculated on the basis of the amount that a low pass filtered signal of the short-term correction value is out of a predetermined range.
The acceleration correction value is a correction value that is proportional to a change of load of an engine.
When the engine condition is in throttle valve off-state, in order to prevent the amount of fuel supplied from changing dramatically and thereby preventing stability of engine operation from deteriorating, the I-gain and P-gain are set to be less than when the engine condition is in throttle valve on-state.
Therefore, when accelerating from an initial throttle valve off-state, there may exist a duration when exhaust gas is lean, because the I-gain, being calculated on the basis of the integration value, is slow to increase.
FIG. 4 is a graph showing engine operation when accelerating from a throttle valve off-state at a vehicle speed of 20 km/h according to prior art.
As shown in FIG. 4, normally an O2 sensor outputs a signal of a rich state when an engine is driven with a throttle valve off. This is because a base amount of fuel is set high to compensate for unstable combustion caused because an engine speed is high and engine load is very low.
In such a throttle valve off-state, an I-gain, used to calculate correction value, is set low.
Therefore, at the time the engine state is changed to a throttle valve on-state, the O2 sensor detects lean exhaust gas because insufficient fuel is supplied even though an acceleration correction value is counted because the I-gain is initially set excessively low.
Moreover, exhaust gas is maintained lean until the I-gain is increased sufficiently because the I-gain is increased gradually.
Furthermore, the duration of the lean state of the exhaust gas, in which state a lot of nitrogen oxides (NOx) are exhausted, is expanded because the I-gain is increased gradually, and in that duration the output power of the engine is reduced.
In addition, especially in an early state of engine operation, a hesitation phenomenon whereby the engine nearly stalls on acceleration, occurs because of a lack of wetted fuel on the walls of the air induction system causes a further lack of supplied fuel.
The present invention has been made in an effort to reduce noxious exhaust gasses and to improve output power of an engine at the same time by improving fuel supply control.
It is an objective of the present invention to provide a method and a system for controlling fuel supply of a vehicle on acceleration for quickly changing an amount of fuel supplied according to vehicle driving conditions by modifying values of feedback gains, and for determining an additional amount of fuel if a lean duration of exhaust gas exceeds a predetermined duration.
To achieve the above objective, the present invention provides a system and a method for controlling fuel supply of a vehicle on acceleration, wherein the system comprises a vehicle speed detector, an engine speed detector for detecting speed of engine revolution, a throttle valve open-angle detector, an O2 sensor for detecting a lean/rich state of exhaust gas, an injector for injecting fuel into the engine, and a control unit that receives signals from the detectors and the O2 sensor and controls an amount of fuel supplied by driving the injector on the basis of the received signals, wherein the control unit performs a method for controlling fuel supply according to the present invention.
The method according to the present invention, in which the control unit calculates a base amount of fuel, receives an output voltage of an O2 sensor, and then calculates a P-gain on the basis of a voltage difference between the output voltage and a predetermined reference voltage, an I-gain on the basis of an integrated value of the voltage difference, and short-term and long-term correction values on the basis of the I-gain and the P-gain, comprises determining whether the vehicle is being accelerated, determining whether the I-gain is in a predetermined range if it is determined that the vehicle is being accelerated, modifying the I-gain and the P-gain if the I-gain is determined to be out of the predetermined range, calculating the long-term correction value on the basis of the modified I-gain and P-gain, calculating a total amount of fuel supplied on the basis of the long-term correction value, and driving an injector on the basis of the calculated total amount of fuel supplied.
Preferably, the step of modifying the I-gain and the P-gain modifies the I-gain by multiplying a difference between the I-gain and a reference I-gain by a first predetermined coefficient and then adding the reference I-gain, and modifies the P-gain by multiplying a difference between the P-gain and a reference P-gain by a second predetermined coefficient and then adding the reference P-gain.
The step of calculating a total amount of fuel supplied entails multiplying the base amount of fuel by the I-gain and the P-gain and then adding an acceleration correction value that is proportional to an amount of change in throttle valve open-angle.
It is also preferable that a method for controlling fuel supply according to the present invention further comprises calculating an additional amount of fuel if a detected duration of inversion exceeds a predetermined duration, wherein the step of calculating the total amount of fuel entails multiplying the base amount of fuel by the I-gain and the P-gain and then adding the additional amount of fuel and an acceleration correction value that is proportional to an amount of change in throttle valve open-angle.
The additional amount of fuel is calculated using the product of the inversion duration and a predetermined conversion factor, the sign of the conversion factor being defined according to the type of inversion among lean to rich inversion and rich to lean inversion.